In the production phase of an oil well, it is usually necessary to artificially lift the crude oil from its natural level in the wellbore to the wellhead. The two most common lift methods are to use either a surface pumping unit or a subsurface rotary pump. A familiar sight in the oil fields around the world is the conventional beam pumping unit (pump jack). This method of bringing oil to the surface accounts for between 70% to 80% of the artificial lifting of oil. The pumping unit may be powered by either an electric motor or an internal combustion engine. In either case it is usually necessary to couple the motor and pump through a speed reducer. A reduction of 30 to 1 is typically needed to operate the pump at 20 strokes per minute (spm). The rotation of the prime mover is converted into an up-and-down motion of the beam and horse head through a pitman/crank assembly. The oscillating horse head of the pumping unit raises and lowers a sucker rod and reciprocates the sucker rod pump in the wellbore. This action lifts the oil on the upstroke to the wellhead.
During production it is often necessary to inject a treatment chemical into the annular space between the well casing and tubing. These might include demulsifiers, corrosion inhibitors, scale inhibitors, paraffin inhibitors, etc. Demulsifiers are chemicals used to dehydrate crude oil containing emulsified water. In many cases this water-in-oil emulsion is very stable. Without the use of a demulsifier, the water would not separate from the crude oil. The rapid separation of the water from the oil phase may be necessary at the well site because of limited storage capacity. The combined total of water remaining in the crude oil must be below 1% in most cases. Excess water can cause serious corrosion problems in pipelines and storage tanks. In addition, water in a refinery stream can interfere with the distillation process and damage the refinery equipment.
In wells which use a production pumping unit, a small chemical pump may be used to inject the treatment chemical into the wellhead. Several types of chemical pumps are known in the art. For example, a pneumatically powered system creates motor force by utilizing compressed air or gas to power a motor. The motor applies forces to a plunger or diaphragm which in turn inject chemical into the well at a measured rate. Another example is electrically powered systems. These systems create motor force by utilizing municipal electricity to power an electrical motor. The motor applies force to a plunger or diaphragm which in turn injects the chemical. A variant of the electrically powered system is a solar powered system which utilizes solar cells to create electricity. The electrical current is stored in a battery bank which in turn powers a DC electric motor. Sealed gel or a matted glass batteries are required due to deep cycle requirements of the environment. Furthermore, these systems must be designed to operate without sunlight for extended periods of time up to thirty days in locations such as Canada, Northern Russia or the Artic.
In solar powered systems extended delays without sunlight due to cloudy weather or location can create a problem for maintaining battery voltage and therefore proper chemical injection rate.
It is therefore extremely important to provide reliable battery service for chemical injection pumps for pump jacks. However, as with other mechanical systems of the pump jack, routine maintenance is required to assure battery performance. The routine maintenance is difficult to provide because the battery usage varies widely from installation to installation. In the prior art, to assure battery performance an operator is required to periodically travel to the installation and test the batteries to prevent failure. Repeated travel to the installation raises costs and reduces profit. Similarly, neglected batteries can easily cause injection failure with concomitant losses in production or efficiency.